As examples of processes for manufacturing biomass based products, manufacturing of reconstituted biomass-based products such as Medium Density Fibreboards (MDF), Particleboards (PB), Oriented Strand Boards (OSB) and the like products can be mentioned. Such manufacturing is basically made in processes as schematically shown in FIG. 1a-c and described below. Similar processes are used when producing pulp and paper products.
As a basis of this processes, a raw material in the shape of timber in the form of round wood or wood chips from the forest, or wood residuals in the form of sidings, chips, shavings or sawdust from the wood industry (sawmills, house and furniture industry etc), or recycling wood and wood based materials, or various kinds of agricultural crop residuals such as bagasse (sugar cane residuals), straw etc, is provided.
Basically, manufacturing of reconstituted biomass products such as MDF, PB and OSB comprises the process steps of disintegrating (cutting, milling etc.) the raw material into particles of various size and shape (fibres, particles, strands), drying of these particles to a moisture content suitable for the specific process, applying a binder (usually a thermosetting binder) to the particles, forming the furnish of particles into a mat and finally pressing and curing said mat into a plate-shaped product such as MDF, PB, OSB or the like board or panel.
As the process steps and the succession of the process steps are different for the above mentioned products, the process flow of the 3 products is commented accordingly in the following.
Medium Density Fibreboards (MDF) Manufacturing.
In traditional MDF manufacturing wood chips, preferably on the basis of debarked solid wood are used as raw material;
Bark residuals and dirt are removed from the chips in a chip washer. Using a chip washer to remove dirt and bark residuals requires large amounts of clean water and produces large amounts of contaminated water, handling of which is a very costly process;
The wet chips are milled into fibres in a disc refiner. Milling the biomass chips into fibres in a disk refiner requires large amounts of electric energy and mechanical wear of machinery;
Usually, an aqueous solution of binder is added to the wet fibre furnish in the so-called blow-line at the outlet of the refiner. In the blow line, the fibre furnish tend to agglomerate to large lumps and the binder added in this stage of the process has very limited access to the single fibres;
The fibre-binder mixture is dried in an airborne drying process using hot air as a heating and transportation medium. Also during drying the fibres in an air-borne process the fibres tend to agglomerate and thus make drying inefficient. Additionally, the transfer of heat energy into the fibres and of water vapour out of the fibres is limited by the laminar boundary layer on the surface of the fibres. Alternatively, other techniques to add the binder to the fibre after drying (see e.g. Danish patent application PA 200401297 and patents quoted herein) are used in MDF manufacturing. Application of binder to the fibre furnish after drying is a more modern approach, the efficiency of which, however, in terms of binder distribution on the single fibres is limited by the tendency of the fibres to once again agglomerate to large lumps;
After drying and application of binder, the fibre furnish is screened, usually in an airborne system, in order to remove larger fibre agglomerations, which may cause damage in the hot press. Screening of the fibre furnish to remove fibre lumps is a costly process in terms of equipment, energy and loss of material; Subsequently the fibre furnish is formed into a homogeneous mat, either by an airborne or a mechanical device. Forming of the fibre mat in conventional formers establishes a 2-dimensional orientation of the fibres in the plane of the mat;
Preheating of the fibre mat by introducing steam or hot air or a mixture of steam and hot air Into the surface of the mat may be made.
Finally, the mat is pressed and cured in a hot press.
Particleboard (PB) Manufacturing.
In Particleboard manufacturing, a wider variety of low quality raw material is used (wood residuals, recycling wood, agricultural biomass etc.;
Screening into coarse and fine particles. The efficiency of screening biomass particles by means mechanical sifters or air-borne equipment is limited by the tendency of fine particles and dirt to stick to larger particles;
Large particles are flaked into proper size;
The particle furnish is dried, usually in drum dryers using hot gas as a heating medium and mechanical devices as a transportation medium. Traditional drying of biomass particles in drum dryers using hot air as a heating medium is limited by the laminar boundary layer at the surface of the particle;
The dry particle furnish is usually separated into a fine fraction to be used for the panel surface and a coarse fraction to be used for the panel core. Separation of coarse and fine particles by traditional mechanical or air-borne techniques is limited by the tendency of these particles to stick together;
A binder is added to these fractions separately in mechanical blenders;
The fractions of particle furnish are formed into a 3-layer mat.
Preheating of the fibre mat by introducing steam or hot air or a mixture of steam and hot air into the surface of the mat may be made;
The mat is pressed and cured in a hot press.
Oriented Strand Boards (OSB) Manufacturing.
Oriented Strand Boards (OSB) are made from regular, debarked round wood from the forest;
The logs are cut into thin (0.5-0.7 mm), wide (20-25 mm) and long (100-150 mm) strands;
Cleaning of the strands from dirt and bark contamination is made in a dry process in mechanical sifters. The efficiency of traditional cleaning of strands from dirt and bark contaminations in mechanical sifters is limited by the adhesion of fine particles to the rough surface of the strands;
Drying of strands is made in drum dryers using hot gas as a drying medium and mechanical devices for transportation of the strands. Traditional drying of strands in drum dryers using hot air as a heating medium is limited by the laminar boundary layer at the surface of the strands;
Application of binder in the form of a powder or an aqueous solution of resin is made in rotating drums;
Forming of strands into a mat is made in mechanical devices, orientating the strands into 3 layers parallel and perpendicular to the process direction respectively;
Preheating of the fibre mat by introducing steam or hot air or a mixture of steam and hot air into the surface of the mat may be made;
The mat is pressed and cured in a hot press.
Within the above listed part processes of manufacturing of biomass-based panel board products a number of problems with relation to the boundary layer between the biomass particles and the surrounding process air flow was identified.
Equipment involving turbulent air flow to deal with said problems are pre dominant in known methods.
Other problems with relation to separating particles of various size and shape or particles and contaminations are usually dealt with using equipment based on mechanical vibration or washing water.
Therefore, it is an object of the invention to provide a system (and a corresponding method) for manufacturing biomass-based products having enhanced efficiency.
It is a further object to provide a method and system enabling efficient separation of fibre lumps so they do not lump or stick together in an airflow.
Another object is to enable enhanced forming of fibres into a mat and improved quality of the final product.
Another object is to reduce the consumption of energy in manufacturing biomass-based products.
In the following, novel methods based on a different kinetic technology and corresponding equipment to handle biomass and other particles will be disclosed.